1. Field of the Invention
The invention is directed to a method for measuring the imaging dose in the framework of the pickup of a radiation image of a subject, particularly an x-ray image, whereby a radiation source is employed for generating radiation, a solid-state radiation detector is employed for image pick up, and a sensor is employed for determining the imaging dose.
2. Description of the Prior Art
In medical x-ray diagnostic installations that serve the purpose of generating radiation images and wherein the determination of the imaging dose is required in order to expose the patient under examination to only the minimally required x-radiation, an ionization chamber is employed for determining the imaging dose. This is arranged in the region of the solid-state radiation detector (with reference to the direction of the incident radiation) and should be as radiation-transparent and shadow-free as possible, so that it is not imaged thereon. The functioning of the ionization chamber is then such that, due to the x-radiation in a charged air capacitor, it generates a current usually lying in the pico-ampere range that is proportional to the dose. Measuring the pico-ampere current is difficult and is particular difficult when the ionization current drops into the femto-ampere range given employment of correspondingly low tube operating voltages. Further problems in the employment of ionization chambers are that the signal of the ionization chamber is determined by the air density in its interior, i.e., the air pressure and the temperature of the measuring chamber must be known and the chamber signal must be corrected by counter-measures in order to be able to determine the correct imaging dose.
The publication. "Bildgebende Systems fur die medizinische Diagnostik". H. Morneburg, Ed., Publicic MCD, 1995, pp. 282-283, discloses the arrangement of a semiconductor radiation detector for dose measurement behind a film cassette in which an X-ray film is arranged.